The present invention generally relates to a polishing slurry dispenser in a chemical mechanical polishing apparatus and more particularly, relates to a polishing slurry dispenser in a chemical mechanical polishing apparatus that is equipped with a plurality of nozzles each having a flow control valve.
Apparatus for polishing thin, flat semiconductor wafers is well-known in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semi-conductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head rotates or oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head; a wafer unload station; or, a wafer load station.
More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. CME apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is xe2x80x9cplanarizedxe2x80x9d or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
A perspective view of a typical CMP apparatus is shown in FIG. 1A. The CMP apparatus 10 consists of a controlled mini-environment 12 and a control panel section 14. In the controlled mini-environment 12, typically four spindles 16, 18, 20, and 22 are provided (the fourth spindle 22 is not shown in FIG. 1A) which are mounted on a cross-head 24. On the bottom of each spindle, for instance, under the spindle 16, a polishing head 26 is mounted and rotated by a motor (not shown). A substrate such as a wafer is mounted on the polishing head 26 with the surface to be polished mounted in a face-down position (not shown). During a polishing operation, the polishing head 26 is moved longitudinally along the spindle 16 in a linear motion across the surface of a polishing pad 28. As shown in FIG. 1A, the polishing pad 28 is mounted on a polishing disc 30 rotated by a motor (not shown) in a direction opposite to the rotational direction of the polishing head 26.
Also shown in FIG. 1A is a conditioner arm 32 which is equipped with a rotating conditioner disc 34. The conditioner arm 32 pivots on its base 36 for conditioning the polishing pad 38 for the in-situ conditioning of the pad during polishing. While three stations each equipped with a polishing pad 28, 38 and 40 are shown, the fourth station is a head clean load/unload (HCLU) station utilized for the loading and unloading of wafers into and out of the polishing head. After a wafer is mounted into a polishing head in the fourth head cleaning load/unload station, the cross head 24 rotates 90xc2x0 clockwise to move the wafer just loaded into a polishing position, i.e. over the polishing pad 28. Simultaneously, a polished wafer mounted on spindle 20 is moved into the head clean load/unload station for unloading.
A cross-sectional view of a polishing station 42 is shown in FIGS. 1B and 1C. As shown in FIG. 1B, a rotating polishing head 26 which holds a wafer 44 is pressed onto an oppositely rotating polishing pad 28 mounted on a polishing disc 30 by adhesive means. The polishing pad 28 is pressed against the wafer surface 46 at a predetermined pressure. During polishing, a slurry 48 is dispensed in droplets onto the surface of the polishing pad 28 to effectuate the chemical mechanical removal of materials from the wafer surface 46.
An enlarged cross-sectional representation of the polishing action which results form a combination of chemical and mechanical effects is shown in FIG. 1C. The CMP method can be used to provide a planner surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An outer layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing, a metal oxide layer can be formed and removed repeatedly.
During a CMP process, a large volume of a slurry composition is dispensed. The slurry composition and the pressure applied between the wafer surface and the polishing pad determine the rate of polishing or material removal from the wafer surface. The chemistry of the slurry composition plays an important role in the polishing rate of the CMP process. For instance, when polishing oxide films, the rate of removal is twice as fast in a slurry that has a pH of 11 than with a slurry that has a pH of 7. The hardness of the polishing particles contained in the slurry composition should be about the same as the hardness of the film to be removed to avoid damaging the film. A slurry composition typically consists of an abrasive component, i.e, hard particles and components that chemically react with the surface of the substrate.
For instance, a typical oxide polishing slurry composition consists of a colloidal suspension of oxide particles with an average size of 30 nm suspended in an alkali solution at a pH larger than 10. A polishing rate of about 120 nm/min can be achieved by using this slurry composition. Other abrasive components such as ceria suspensions may also be used for glass polishing where large amounts of silicon oxide must be removed. Ceria suspensions act as both the mechanical and the chemical agent in the slurry for achieving high polishing rates, i.e, larger than 500 nm/min. While ceria particles in the slurry composition remove silicon oxide at a higher rate than do silica, silica is still preferred because smoother surfaces can be produced. Other abrasive components, such as alumina (A13O2)may also be used in the slurry composition.
The polishing pad 28 is a consumable item used in a semiconductor wafer fabrication process. Under normal wafer fabrication conditions, the polishing pad is replaced after about 12 hours of usage. Polishing pads may be hard, incompressible pads or soft pads. For oxide polishing, hard and stiffer pads are generally used to achieve planarity. Softer pads are generally used in other polishing processes to achieve improved uniformity and smooth surface. The hard pads and the soft pads may also be combined in an arrangement of stacked pads for customized applications.
Referring now to FIG. 2, wherein a perspective view of a CMP polishing station 42 is shown. The polishing station 42 consists of a conditioning head 52, a polishing pad 28, and a slurry delivery arm 54 positioned over the polishing pad. The conditioning head 28 is mounted on a conditioning arm 58 which is extended over the top of the polishing pad 28 for making sweeping motions across the entire surface of the pad. The slurry delivery arm 54 is equipped with a single slurry dispensing nozzle 62 which is used for dispensing a slurry solution on the top surface 60 of the polishing pad 56. Surface grooves 64 are further provided in the top surface 60 to facilitate even distribution of the slurry solution and to help entrapping undesirable particles that are generated by coagulated slurry solution or any other foreign particles which have fallen on top of the polishing pad during a polishing process. The surface grooves 64 while serving an important function of distributing the slurry also presents a processing problem when the pad surface 60 gradually worn out after successive use.
The conventional slurry delivery arm 54 is provided with a single outlet as shown in FIG. 4 or with dual outlets as shown in FIG. 2. A slurry solution is dispensed from the single nozzle to the polishing pad surface in a single flow or droplets of the slurry solution at a single location on the polishing pad. The single nozzle slurry dispensing system further contributes to the non-uniformity in polishing by the polishing pad. For instance, as shown in FIG. 3 of a graph plotted of removal rates of copper polishing against the distance on the wafer surface. It is seen that removal rates vary between about 2894 xc3x85/min. and about 3025 xc3x85/min., i.e. representing a range of about 130 xc3x85/min. or a variation of 4-5%. The variation in removal rates between the center of the wafer and the edge of the wafer is not acceptable and must be remedied.
It is therefore an object of the present invention to provide a slurry dispensing unit for a chemical mechanical polishing apparatus that does not have the drawbacks or shortcomings of the conventional slurry dispensing units.
It is another object of the present invention to provide a slurry dispensing unit for a chemical mechanical polishing apparatus that dispenses a polishing slurry from a continuous, closed-loop flow of the slurry solution.
It is a further object of the present invention to provide a slurry dispensing unit for a chemical mechanical polishing apparatus that does not have a single dispensing nozzle.
It is another further object of the present invention to provide a slurry dispensing unit for a chemical mechanical polishing apparatus that is equipped with a plurality of slurry dispensing nozzles.
It is still another object of the present invention to provide a slurry dispensing unit for a chemical mechanical polishing apparatus that is equipped with a plurality of slurry dispensing nozzles wherein each has a different nozzle opening than the neighboring nozzle openings.
It is yet another object of the present invention to provide a slurry dispensing unit for a chemical mechanical polishing apparatus equipped with a plurality of slurry dispensing nozzles wherein the nozzles have the same size opening.
It is still another further object of the present invention to provide a slurry dispensing unit for a chemical mechanical polishing apparatus equipped with a plurality of slurry dispensing nozzles each provided with a flow control valve.
It is yet another further object of the present invention to provide a slurry dispensing unit for a chemical mechanical polishing apparatus equipped with a plurality of adjustable slurry dispensing nozzles.
In accordance with the present invention, a slurry dispensing unit for a chemical mechanical polishing apparatus equipped with a plurality of adjustable nozzles is provided.
In a preferred embodiment, a slurry dispenser unit for a chemical mechanical polishing apparatus is provided which includes a dispenser body that has a delivery conduit, a return conduit and a U-shape conduit connected in fluid communication therein between for flowing continuously a slurry solution therethrough; and a plurality of nozzles integrally connected to and in fluid communication with a fluid passageway in the delivery conduit for dispensing a slurry solution.
In the slurry dispenser for a chemical polishing apparatus, the plurality of nozzles each has an opening that is the same in size as the openings of its immediately adjacent nozzles. The plurality of nozzles each may have an opening that is different in size than the openings of its immediately adjacent nozzles. The plurality of nozzles each may have an opening that is between about 0.5 mm and about 5 mm in diameter. The plurality of nozzles each has an opening that is controlled by an adjustable flow control valve to provide a slurry dispensing rate between about 0.1 ml/sec. and about 10 ml/sec. The plurality of nozzles may include at least four nozzles, or the plurality of nozzles may include one nozzle for each 12.5 mm spacing on a semiconductor wafer. The plurality of nozzles may include sixteen nozzles when the dispenser is adapted for dispensing slurry on a 300 mm semiconductor wafer. The plurality of nozzles may each have an opening that is controlled by a pneumatically adjusted flow control valve.
The present invention is further directed to a chemical mechanical polishing apparatus for planarizing semiconductor wafers that includes a wafer holder for holding a wafer therein and for rotating, traversing the wafer on a polishing pad; a polishing platen for mounting and rotating a polishing pad mounted thereon; a conditioning arm for operating a conditioning disc mounted thereon and for conditioning a top surface of the polishing pad; and a slurry dispenser that has a body portion of a delivery conduit, a return conduit and a U-shape conduit connected in fluid communication therein between for flowing continuously a slurry solution therethrough; and a plurality of nozzles integrally connected to and in fluid communication with a fluid passageway in the delivery conduit for dispensing a slurry solution.